Panic

On one occasion Bacchus, in his Indian expeditions, was
encompassed with an army far superior to his own; one of his chief
captains, named Pan, advised him to command all his men at the dead of
night to raise a simultaneous shout. The shout was rolled from mountain
to mountain by innumerable echoes, and the Indians, thinking they were
surrounded on all sides, took to sudden flight. From this incident, all
sudden fits of great terror have been termed panies. (See Judges vii. 18-21.)

Theon gives another derivation, and says that the god Pan struck
terror into the hearts of the giants, when they warred against heaven,
by blowing into a sea-shell.